(U)SIM cards are Java capable and there is the Globalplatform that specifies standards API. SMS can be addressed directly to the SIM card, the SIM card will get events for network selection and others, it can modify call establishment attempts.

The following will show how to build the example applet and install it on your USIM. If you create plugins please make them available as Free Software and point us to them. If you find interesting Globalplatform APIs or hacks please talk about it.

Make sure you have the KIC1, KIC2, KIC3 and KID1, KID2 and KID3 for your card. If you have a CCC Event card from 31C3 or later you should be set and for the sysmoUSIM-SJS1 be sure to buy the option that includes the ADM1 keys as otherwise no OTA keys will be provided to you (you will have to buy a new batch of cards then).

Instead of directly interacting with the SIM through a PCSC reader the APDU is sent through SMPP. Replace the --pcsc call with --smpp and lines starting with SMPP are printed. These then need to be sent.